"It sums to "I can tweak my setup and get this part to be good enough relative to the expensive machine." and that is great. What is missing is it is every friggin' part. Seriously, all of the $2,000 printers have quirks that hit based on part geometry, especially in ABS. Part too long? need to add hold down tabs to prevent warping. Too many overhangs? extra supports. Too long a tool travel? Up the hotend temperature so that the extruded material doesn't cool down to much."
No, this is like the crusty machinist who knows just how to wiggle his hips and shake his elbow to get a 1/2 thou on the worn-out bridgeport in the corner.
FDM should let engineers make prototypes without bothering that guy (whose time is probably 3x more valuable than theirs, even if his pay doesn't reflect it). This sounds like the printer is just a more compact version of the worn-out mill.
Plus you have to account for the printer's quirks right in your 3d model which is annoying and error-prone. (Yes, I know every package has a way to segregate those changes, etc. but still.)
The RepRap project and the derived printers tend to share the opposite philosophy - the original idea was to print parts for more printers, so naturally parts were designed to be 3D printed. The RepRap logo is a compromise design for part holes without support (no longer necessary, though).
Most RepRap owners ('hobbyists') are using the 3D printer as the end manufacturing method, not just for prototypes, so this is a pretty reasonable tradeoff. Note that the original article fell into this category - the 3D printed part was not a prototype, but a jig used in production. (looking at that part, it could have been designed to not require any support material at all)
This is called 'mechanical engineering'. :-)